The two basic optical Fourier transform configurations are examined with respect to component complexity, aberrations, and optical noise. It is shown that the converging-beam illumination setup (CB-FT) is much simpler and works better than the classical parallel beam illumination setup within a restricted range of object size and lens aperture. This range corresponds to many practical cases. Therefore, the CB-FT should be preferred in ordinary cases whereas the classical setup with a special purpose Fourier lens should be used only for a large space–bandwidth product. It is probably never a good solution to use the parallel beam configuration with a general purpose lens as the Fourier lens.
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